This invention relates generally to devices for implementing a ground connection between a metallic shield of a cable and a common ground point. More particularly, the present invention relates to clamp devices which mount to service cables and connect via a flexible or rigid conductor with a common ground point.
Service cables, which may be buried underground or suspended above ground, are typically constructed in a tubular fashion with numerous thin metal conductors or pairs of conductors surrounded by a conductive ground shield. The shield is in turn surrounded by a protective jacket of tough, flexible plastic or rubber. The conductive shield of a service cable is intended to prevent electromagnetic fields and lightning from penetrating the cable and interfering with signals being transmitted on the conductors. To function properly and safely, cable shields must be grounded at spaced ground points established by regulations and/or operational specifications and practices. The invention generally relates to clamp assemblies adapted to create and maintain such ground connections.
In applications to which the present invention relates, the clamp assemblies are ordinarily positioned within a cabinet, housing or other enclosure (hereafter collectively termed "enclosure") to provide a grounding connection between the metallic shield of the service cable/s and a common ground point. Such enclosures are frequently located outdoors and/or underground where the enclosures and their contents are subjected to intense environmental changes. For example, it is not uncommon for the enclosure to heave as a result of frost while the service cables are frozen in position in the ground. Moisture in the form of rain, ground water or condensation is also frequently present within the enclosure.
U.S. Pat. No. 5,429,532 discloses one type of cable shield ground clamp to which the present invention generally relates. The clamp is constructed of a generally U-shaped yoke. A keeper has a driver which threadably engages threaded surfaces on the inside of the yoke legs. The keeper has a clamp jaw which may be compressively engaged against a cable shield or shields received in an aperture defined by the yoke. The yoke then connects to a common ground point via a flexible ground wire connection.
As cables are tightened within such a clamp, damage can occur to the conductors within the cable or to the shield surrounding the conductors, or both. It is known in the art to install protective devices within such cable shield/ground clamp assemblies to prevent damage to the cable conductors. U.S. Pat. No. 5,722,840 discloses one type of conductor protector to which the present invention generally relates. The conductor protector takes the form of a protective shoe that may be inserted between the conductors and the cable clamp jaw to prevent crushing of the inner conductors. The protective shoe is an elongated semi-sleeve-like or trough-like member composed of electrically conductive material and having a longitudinally extending channel. The cable may be placed in the channel of the shoe or the shoe may be inserted within the shield. In either configuration, the shoe partially surrounds the inner conductors. The cables are then placed within the clamp and the jaw is tightened. As the jaw compresses the cables, the rigidity of the shoe provides crush resistance while allowing the clamp to be tightened to ensure a mechanical engagement of high integrity.
To install the protective shoe disclosed in U.S. Pat. No. 5,722,840, the protective jacket must be removed from the cable to ensure a proper electrical connection between the cable's conductive ground shield and the ground clamp. While introduction of the conductor protector disclosed in U.S. Pat. No. 5,722,840 presented a significant improvement over industry practice and provided crush resistance and strain relief not previously available, those skilled in the art will recognize that there are drawbacks to removal of the protective jacket. Removal of the protective jacket presents new avenues for moisture to penetrate the cable. Loss of the linear strength and abrasion resistance of the protective jacket weakens the cable and the resulting cable shield/ground clamp assembly. In addition, the process of jacket removal involves scoring around the cable with a sharp knife, often resulting in nicks or cuts in the underlying shield, thus weakening the shield. Such weakened shields are prone to failure and consequent loss of ground continuity. Furthermore, removal of the jacket adds a step to the labor required to install a cable shield/ground clamp assembly.